The Streptomyces are well known producers of a variety of extracellular enzymes including proteases, phosphatases, xylanases, cellulases, amylases, lipases and nucleases.
In addition, members of the genus Streptomyces produce a large number of antibiotics, pigments and other secondary metabolites and have a complex pattern of differentiation resulting in the formation of spores. In batch cultures of Streptomyces there is usually a coincidence in the production of extracellular enzymes and the onset of antibiotic production and pigment biosynthesis and sporulation. All of these processes are repressed by nutritional conditions favoring high growth rates and are derepressed by starvation of P, C or N sources. It is likely that enzyme secretion, formation of secondary metabolites and differentiation are completely independent but respond to similar triggering mechanisms.
Several genes of Streptomyces encoding extracellular enzymes have been cloned. These include agarase from Streptomyces coelicolor, endoglycosidase H from Streptomyces plicatus, xylanase from Streptomyces lividans, alpha-amylase from Streptomyces hygroscopicus, cellulase from Strep. spA2, beta-galactosidase from Strep. lividans and beta-lactamases from Strep. cacaoi, badius and fradiae.
However, the regulatory mechanisms which control expression of these genes are virtually unknown. In addition to specific regulatory mechanisms, such as induction of amylase by dextrins or maltotriose and carbon metabolite regulation of amylase or agarase, general mechanisms of derepression of several extracellular enzymes are likely to occur since simultaneous production of several polymeric-substrate degrading enzymes has been observed in Streptomyces following a nutritional down-shift. Such transacting regulatory genes have been found in Bacillus subtilis (J. BACTERIOL. 169:324-333,1987), Bacillus natto (J. BACTERIOL. 166:20-28,1986), and Bacillus licheniformis.
Positive regulatory genes affecting enzyme synthesis and/or secretion might be cloned by searching for increased secretion of extracellular enzymes in a poor secretory strain such as S.lividans.
Systems for expressing foreign DNA sequences in Streptomyces have previously been described in, for example, EP 148,552 and WO 88/07079. These systems use the endogenous promoters of extracellular enzymes produced by Streptomyces.